Northern Greenland Sea Research Articles

A numerical simulation of the sea ice cover in the northern Greenland Sea

A numerical simulation of the sea ice cover in the northern Greenland Sea (NGS) is presented. The simulation is carried out using the coupled sea ice ocean general circulation model of Oberhuber (1993). The coupled model is forced using monthly climatological atmospheric forcing. The model domain includes both the Arctic Ocean and the North Atlantic. The large‐scale characteristics of the observed sea ice cover in the NGS are reasonably well reproduced when compared with the limited observations available. Two notable aspects of the simulation are (1) a trough in the ice compactness across Fram Strait and (2) a polynya along the northeast coast of Greenland. Both of these features are evident in the observations during the spring‐summer period. A sensitivity experiment in which the ice internal stress term is removed from the ice model demonstrates that the inclusion of a realistic sea ice rheology is a key factor in simulating the detailed features noted above for the NGS.

Photosynthesis of Phaeocystis in the Greenland Sea

During the spring bloom in the northern Greenland Sea in 1989, Phaeocystis displayed photosynthetic rates and efficiencies, absorption in the red, and quantum yields approaching predicted theoretical maxima. Average values of these photosynthetic parameters for Phaeocystis were about an order of magnitude higher than those typically observed for natural assemblages of diatoms which often dominate the phytoplankton in polar waters. Phaeocystis populations were exceptionally well acclimated to temperatures near 0°C and all light conditions encountered. With such high photosynthetic rates and quantum yields, Phaeocystis may outcompete other species and play a dominant role in elemental cycles where major blooms are recurrent features. During Phaeocystis blooms, primary productivity in polar regions would be seriously underestimated by models using previously reported averages.

Species-specific differences in intact wax esters of Calanus hyperboreus and C. finmarchicus from Fram Strait — Greenland Sea

Intact wax esters were studied in the herbivorous calanoid copepods Calanus hyperboreus and C. finmarchicus from the close pack ice region and the marginal ice zone (MIZ) of the Fram Strait in the northern Greenland Sea. Wax esters ranging from 30 to 44 carbon atoms with up to seven double bonds were identified. In the MIZ both species had significantly higher proportions of polyunsaturated wax esters than those in the pack ice zone, as a result of the different nutritional regimes. Despite this spatial variability, pronounced species-specific differences were found. Calanus hyperboreus lipids contained more diunsaturated long-chain wax esters of 38:2, 40:2, 42:2 and 44:2 structure, whereas C. finmarchicus lipids were dominated more by the monounsaturated short-chain wax esters, 34:1 and 36:1. The identification and molecular structure of the wax esters were confirmed by analysing fatty acid and alcohol moieties separately. Only small differences were detected between the wax ester compositions of females and copepodid stages IV and V. There was a tendency towards long-chain wax esters in the older stages.

The structure and atmospheric forcing of the mesoscale velocity field in Fram Strait

We consider the connection between the wind field and the mesoscale circulation in the northern Greenland Sea, using over 50 record years of current observations to define the current structure in space and time. We find that east of the East Greenland Polar Front the motion is highly coherent in the vertical and that it scales in the horizontal as the internal Rossby radius. The structure depends very little on frequency. The East Greenland Current is dominated by smaller‐scale phenomena in both space and time, and the kinetic energy is low. The available energy in the wind field may be the largest in the world, especially over the Greenland and Iceland seas. The wind power shows a marked seasonal signal that east of the East Greenland Polar Front is paralleled by a similar signal in the fluctuating kinetic energy of the current, and the former leads the current fluctuations by 1–2 months. The mesoscale motions are probably dominated by nonlinear interactions, and the observed vertical and horizontal structure is in general agreement with predictions of the theory of quasi‐geostrophic turbulence forced by atmospheric fluctuations. We conclude that the majority of the mesoscale fluctuations in Fram Strait east of the East Greenland Polar Front are generated by the wind field. However, with few exceptions, the current field is not coherent with the curl of the wind stress, probably primarily owing to the isolating effect of the rough topography. The extent to which the wind field also generates mesoscale motions in the East Greenland Current is uncertain, although the eddy kinetic energy east of the East Greenland Polar Front is probably sufficient to account for conditions in the East Greenland Current by westward advection of eddies.

Surface‐based passive microwave studies of multiyear sea ice

Multifrequency passive microwave observations are reported from surface based field experiments carried out over multiyear sea ice in the eastern Arctic Basin, the Beaufort Sea, the Canadian archipelago and the northern Greenland Sea. Dual polarized brightness temperatures at 6.7, 10, 18.7, 37, and 90 GHz were obtained at selected multiyear ice sites covering a wide range of surface properties. Considerable variation was found in the observed spectra over short distances on individual floes under winter conditions where values of [ev(37 GHz) − ev(18 GHz)]/[ev(37 GHz) + ev(18 GHz)] ranged from nearly zero to approximately −0.08. Concurrent surface characterization observations consisting of temperature, density, salinity, and grain size profiles in the snow and the upper meter of the ice were carried out frequently in conjunction with Cold Regions Research and Engineering Laboratory personnel. The present analysis shows that the magnitude of the spectral gradient of emissivity is directly related to the existence and thickness of a decomposed surface ice layer with very high porosity. Spectra for melt ponds with a frozen surface layer closely resembled those of lake ice and show a positive spectral gradient. As soon as the ponds were completely frozen, their spectra became nearly the same as those for first‐year ice. Fine‐grained winter snow produced a mild decrease in the emissivities at 90 GHz with increasing snow thickness from 0 to 0.2 m at which point the snow appears to be optically thick. During the melt season the ice emissivities eν depend most strongly on whether the surface layers are experiencing temporary freezing or not. Under melting conditions, eν depends on the liquid water content only over a very small range (e.g., 0–5% by mass at 90 GHz). If the liquid water in the surface layers is freezing, which can occur at intervals throughout the melt season, the spectral gradient is negative with a slope which depends on the thickness of the refrozen layer. The variance among emissivity spectra for multiyear ice appears to be influenced primarily by the distribution of melt ponds and by the presence of significant amounts of scattering inhomogeneities greater than 1 mm in diameter in the snow and in the upper 20–30 cm of the ice. We expect the signatures of multiyear ice to be regionally dependent, perhaps yielding environmental information about the Arctic ice pack.

Seasonal variations in the West Spitsbergen Current estimated from bottom pressure measurements

From 1982 to 1985 two pressure gauges were deployed across the continental shelf northwest of Spitsbergen to determine the seasonal variations in the barotropic component of the West Spitsbergen Current. The variation in current velocity was calculated after analysis and removal of the tidal signals and correction of the pressure difference across the 47‐km section for bottom buoyancy effects. The pressure‐derived velocity fluctuates about 10 cm s−1 peak to peak with the maximum northward flow occurring in the winter. The maximum appears to the correlated with the seasonal cycle of wind stress curl in the northern Greenland Sea. In fact, the magnitude of the velocity variation corresponds to the Sverdrup transport due to the fluctuation in wind stress curl at 79°N, 7.5°E. The idea that the observed variation might also be due to the spin‐up of the basin by wind stress curl is explored with two simple analytical models. Basin spin‐up does appear to be a possible cause. However, East Greenland Current velocity data from Muench et al. (1986) indicate that the fluctuation about the mean in the deep currents on the western side of the basin is northward in winter, while basin spin‐up would produce a southward fluctuation. This supports the idea that Sverdrup transport dominates basin spin‐up, at least at the margins of the basin. The fluctuations in transport and heat flux though the pressure gauge section are estimated to be 2 Sv and 30 to 60 TW peak to peak. These values are major fractions of historical estimates of the mean transport and heat flux values in the West Spitsbergen Current, and they are significant fractions of the total oceanic fluxes into the Arctic Ocean. This suggests that long time series are required to make meaningful estimates of the heat budget of the Arctic.

Late Neogene climate evolution of the central Arctic Ocean

Because no sediment of post-Eocene to Late Miocene or Pliocene age has been recovered from the central Arctic Ocean, oceanographic conditions during the middle Cenozoic are unknown. The oldest late Cenozoic sediment is glacial-marine and contains agglutinated foraminifera. A few calcareous organisms are present in the oldest late Cenozoic sediment (with an age of 2–4 Ma) but at approximately the time as deposition of lithostratigraphic unit F, sometime between 2.0 and 1.5 Ma, there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central Arctic Ocean. Many of the newly introduced species are Atlantic in origin. Preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the Arctic Ocean CCD level and this may be explained by increased circulation with the Northern Greenland Sea. Details of the change in threshold values in the Fram Strait required for the introduction of relatively warmer and carbonate-rich water into the central Arctic Ocean are unknown. There is evidence that spreading rates along the North Atlantic-Nansen Ridge System increased during the Pleistocene and this may have permitted increased circulation between the North Atlantic and the central Arctic Ocean. This important change in Arctic Ocean circulation corresponds to increased Pleistocene seasonality in the Northern Hemisphere.

Relationships of food uptake and body components of Calanus finmarchicus, C. glacialis and C. hyperboreus to particulate matter and water characteristics in Fram Strait

During MIZEX'83 and MIZEX'84 food composition and food uptake by three Calanus species were investigated in the northern Greenland Sea. Samples were obtained from open water, the marginal ice zone, the pack ice region and the East Greenland shelf polynya. Food uptake of Calanus spp. was determined in ship-board incubation experiments under in situ conditions and volume of particulate matter in the upper 300 m of the water column was measured. Principal components analysis was used for data evaluation. Under the pack ice strongly reduced amounts of particulate matter in the euphotic zone were found while concentrations were elevated in the marginal ice zone and the East Greenland shelf polynya. Food uptake of C. finmarchicus was correlated to food concentration. In the pack ice region ingestion was close to zero for all species investigated. Likewise body weights were significantly lower than in MIZ or polynya. Principal components analysis of physical data shows a clustering of MIZ station groups at high temperature and salinity, clearly separated from pack ice and polynya stations. Analysis of biological data results in the same grouping of stations demonstrating a strong influence of hydrographic conditions on plankton development. It is concluded that herbivorous copepods cannot sustain themselves in the pack ice region but only at places of high productivity like marginal ice zone and East Greenland shelf polynya.

A study of oceanic surface heat fluxes in the Greenland, Norwegian, and Barents Seas

This study examines oceanic surface heat fluxes in the Norwegian, Greenland, and Barents seas using the gridded Navy Fleet Numerical Oceanography Central surface analysis and the First GARP Global Experiment (FGGE) IIc cloudiness data bases. Monthly and annual means of net and turbulent heat fluxes are computed for the FGGE year 1979. The FGGE IIb data base consisting of individual observations provides particularly good data coverage in this region for a comparison with the gridded Navy winds and air temperatures. The standard errors of estimate between the Navy and FGGE IIb winds and air temperatures are 3.6 m/s and 2.5°C, respectively. The computations for the latent and sensible heat fluxes are based on bulk formulas with the same constant heat exchange coefficient of 1.5×10−3. The results show extremely strong wintertime heat fluxes in the northern Greenland Sea and especially in the Barents Sea in contrast to previous studies. The highest monthly average net fluxes are well over 400 W m−2 in these two regions in January and February 1979. The estimated uncertainty for the higher heat fluxes based on the comparison between the FGGE IIb and the Navy data sets is about ±30%.

The western Svalbard margin (74°–80°N)

A regional study of the continental margin between the Senja and Molloy-Spitsbergen fracture zones reveals that the transition from continental to oceanic crust occurs in a narrow zone beneath the outer shelf and uppermost slope. The postulated continent-ocean boundary appears to be fault-related consisting of sheared and rifted segments. The marginal structures are compatible with a plate tectonic model in which the southern Greenland Sea opened along a northeasterly propagating plate boundary in the Eocene, whereas the northern Greenland Sea started opening in the early Oligocene. The main structure at the margin is the Hornsund Fault Zone which probably reflects an old zone of weakness rejuvenated in the Tertiary, first by shear and later by extensional movements. In the early Tertiary local transpressional and transtensional components along the plate boundary are associated with the Spitsbergen Orogeny, emplacement of belts of high-density oceanic crust and tectonism in the western Barents Sea. A complex volcanic rifted margin characterized by the Bjørnøya Marginal High links the predominantly sheared margin segments on either side. The main ridge-like segment of the Hovgaard Fracture Zone was originally part of the Spitsbergen margin. In a regional sense, the Hornsund Fault Zone demarcates the eastern boundary of the Tertiary sedimentary wedge which reaches a total thickness of more than 7 km. There appears to have been a considerable increase in deposition of sediments the last 5–6 my. Depocentres located seaward of the east-west fjord systems and submarine depressions indicate a relationship between late Cenozoic glaciations and high sedimentation rates.

Pleistocene paleoceanographic correlations: Northern Greenland Sea to central Arctic Ocean

Correlation of Pleistocene paleoceanographic events across parts of the polar seas is accomplished with core MG-123, from the Swedish YMER-80 cruise. The 8.72 m sediment core, one of the longest recovered from any part of the Arctic Ocean, contains abundant microfossils and coarser grain sediment that are useful in interpretation and correlation of Pleistocene events with shorter sediment cores in the central Arctic Ocean. Faunal and sediment correlations are constrained by δ 18O correlations and a time series analysis that matches several possible sedimentation rates for MG-123 with central Arctic Ocean sedimentation rates and provides a best fit correlation of the cores. The results of this study provide the first correlation of northern Greenland Sea (=southern Arctic Ocean) sediment with that of the central Arctic Ocean, more than 1000 km distant. Oceanic circulation patterns between the areas during the Pleistocene involved increased circulation during interglacials with reduced circulation during glacials. Subpolar water was not present in the northern Greenland Sea during the past 600,000 years. During this time, alternating phases of the climate cycle show a strong relationship to the 100,000 year Milankovitch cycle.

Surface-Based Passive Microwave Observations of Sea Ice in the Bering and Greenland Seas

Measurements of brightness temperatures of sea ice were carried out during both the MIZEX field experiments in 1983, the first in Februrary in the Bering Sea and the second in June/July in the northern Greenland Sea. In the Bering Sea thin growing sea ice types from black ice to 400-mm-thick snow-covered floes were investigated. Brightness temperatures increased with ice thickness up to 100 mm from values of 100 K for open water to as high as 250 K (e= 0.97) for thick ice, and a moderate dependence on snow thickness was found. In the Greenland Sea thick first-year and multiyear ice types were studied. Brightness temperatures were quite variable depending on the daily melt-freeze cycle superimposed on the seasonal warming, ranging from near blackbody values for melting conditions to multiyear-like spectra when the surface layers refroze. The melt season was sufficiently advanced, however, that first-year and multiyear ice could not be differentiated radiometrically.